So does this mean my Early 2011 15" MacBook Pro won't be able to use my iPhone as a relay for SMS and voice calls, or is that separate from where the devices allow you to continue certain tasks on the other?
Same exact model as you.
I think SMS/Voice Calls will still work. Handoff is explicitly over bluetooth and Apple (rightly) wants this to happen over Bluetooth LE. The SMS/Voice likely works over wi-fi.
There's a very practical reason for the difference.
Handoff implies you were working with one device and now you're near another (iPhone to desktop, iPad to iPhone, etc.) and Bluetooth LE is perfect for this use scenario.
Answering phones and receiving SMS implies you're in your home, your phone could be in the other room, and you need to reply or answer from another device. Bluetooth would run into problems handling such use distances but routing things through your Wi-Fi network is a breeze.
So TL;DR: SMS/Voice is likely over wi-fi (or a network, in case your Mac is connected via ethernet) and is likely coming to all devices getting Yosemite.
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ADDENDUM:
While Handoff is a nice feature, likely most people will not upgrade for this feature alone. I mean honestly, you start a draft or work on a document, you want to spend another $1k just to have the ability to click a dynamic link to open the work on your Mac?
My early 2011 MBP should last till 2017 (to answer another post), only last year did I retire the 2006 MBP we had and upgraded the wife to a 2013 MBA.